Electric heater



April 18, 1933. c. c. ABBOTT ELEGTRIG HEATER Filed May 15, 1930 Inventor: Charles CLAbbott,

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vPatented Apr. 18, 1933 UNITED ,STATES PATENT OFFICE CHARLES C. ABBOTT, OF PITTSFIELD, MASSACHUSETTS, ASSIGNOR TO GENERAL ELECTRIC COMPANY, A CORPORATION NEW YORK ELECTRIC HEATER Application filed Hay 15,

My invention relates to electric heaters and has for its object the provision of a simple, rugged and compact heater of inexpensive construction.

More particularly my invention relates to electric heaters of the type wherein a resistance heating conductor is embedded in heat insulating material in a metallic sheath, and more especially to a form of heater which is adapted for use as a space or air heater.

For more complete understanding of my invention reference should be had to the accompanying drawing in which Fig.. 1 is a plan view, partly in section, of an electric heater embodying my invention; Fig. 2 is an elevation view, partly in section, of the lieater shown in Fig. 1; Figs. 3, 1 and 5 are views showing detailsof construction; Fig. 6 is a diagrammatic view illustrating the method of assembly; while Fig. 7 is a fragmentary sectional view showing a modified form of my invention.

Referring to the drawing, one of the objects of the invention is to provide aheater having a fairly large surface area which is uniformly heated, and to this end a helical resistance conductor or heating resistor 10 is provided and arranged ,in a plurality of lengths extending back and forth between two supporting insulators 11 and 12 'made of a suitable heat refractory material, such as porcelain. As shown, the resistance conductor extends back and forth in four parallel lengths lying in a common pla-ne. Preferably the turns of the two inner lengths are spaced farther apart than the turns of the two outer lengths so as to reduce the rate of heat generation in the middle and thereby provide a uniform temperature through- 4 out the heater. rI`he heating resistor and the supporting insulators 11 and 12 are in turn enclosed i'n a metallic sheath 13 of oblong or rectangular cross-section, the resistance conductor being embedded in compacted,

powdered, heat refractory insulating material 14, such as magnesium oxide.

Thesup orting insulators 11 and' 12 as viewed in ig. 1, are rectangular in shape, their thickness as indicated i'n Fig. 2, being only a fractional part of their plan dimen- 1930. Serial No. 452,750.

sions. Each is provided with a series of grooves on its upper face, that is, the face exposed or uppermost in Fig. 1, to provide for securing the resistance conductor in place. It will bc observed that the insulator 11 is grooved so as to provide protuberances l5 and 16 extending parallel with the lengths of the resistance conductor and adjacent opposite sides of the heater; This construction of the insulator also leaves a central protuberance 17 which serves to separate the adjacent lengths of the resistancev conductor. The protuberances 15v and 16 are provided with inclined or over-hanging ends 15a and 16a forming projections overhanging the re` CYD vsistance conductor so as to secure it in place,

as will readily be observed from an examination of Fig. 2. The outer end ofthis in sulator 11 is also provided with a dovetail extension 18 which serves as a means for supporting the insulator during the assembly of the unit as will hereinafter be pointed out.

While similar to the insulator 11, the construction of the supporting insulator 12 at the.` opposite end of the sheath, is somewhat different in detail. Like the insulator 11, it is provided with a dovetail extension 12a. It is also provided with four slots 19, 20, 21 and 22 in its inner end to receive the ends of the resistance conductor 10. As shown, the two eXtreme ends of the resistance conductor lie in the slots 19 and 22 and are secured respectively to metallic terminals or terminal members 23 and 24.

The terminals 23 and 24 are shown in detail in Fig. 3 and the connection between each terminal and the end of the resistor will be understood from an examination of this figure and Fig. 2. The shank of the terminal is provided with an elongated recess 25 into which the end of the resistor is inserted. Before inserting the end of the resistor a short metallic pin 26, having approximately the same diameter as the inside diameter of the resistor coils, is inserted in the end of the resistor after which the resistor and the pin are inserted in the recess and the shank of the terminal then compressed or swaged down over the turns of resistor wire where- 100 by a oodA mechanical connection as well as a oo electrical connection is formed.

ecesses are provided for the terminals in the insulator 12, the Shanks of the terminal members lyin in the inner ends of the slots 19 and 22. central bore 27 into which the threaded ends of the terminal pins 29 and 30 are screwed tightly so as to clamp the terminal pins and the terminal lugs securely to the casing 13, this connection bein Lshown in detall in Fig. 2. The termina s are separated electrically from the sheath 13 by means of an insulator 31 which is preferably rectangular in form and is seated in a recess provided for it in the top of the insulator 12. It is, of course, provided with apertures registering with apertures in the sheath through which the terminal pins extend. In a simllar mannerthe terminal pins are electricall insulated from the sheath by means o disc insulators 32, the pins being provided with shoulders which engage with washers 33, which in turn rest on the insulators 32. An insulating washer 34 fits in each aperture in the sheath thereby holding the pins 29 and 30 centrally in the aperture. These various parts are secured rigidly together by screwing the terminal pins tightly into the terminal lugs. The insulators 31, 32 and 34 are preferably made of mica. v

As shown, the slots 2O and 2l are connected together attheir inner ends so as to leave a projection 35 around which the central ortion of the resistor is passed and there y secured. Preferably the end of the projection nearest the end of the heater is formed with ri ht angle-sides, the opposite vwalls of the sot of course bein parallel therewith to receive a right ange resistor securing member 36 shown in detail in Fig. 5. This member, as shown in Fig. 1, is placed over the resistor Where it passes around the projection 35 so as to hold the resistor in place. As shown in Figs. 4 and 5, the lower side of the locking member is provided with a recess 37 to receive the turns of the resistor.

In the arrangement shown the resistance conductor 10 is arranged in three loops pass'- ing respectively around the protuberances 15, 16 and 35. Obviously where aheater having different characteristics is desired, for example, a lower rate of heat output, the

.resistance conductor may sim ly extend in a single loop, or a plurality o loops may be connected in parallel for a higher rate of heat output, the insulators 11 and 12 being suitably -constructed Vt0 provide for this arrangement. An indentation 38 is provided in the insulator 11 and the sheath 13 is struck down `into this `indentation as indicated by the reference numeral 39 in order to secure the insulator 11 against movement lengthwise of the sheath. This may be taken care of, however, by making the indent in the ach terminal has a threaded them.J The ends of the resistance conductor with the terminals 23 and 24 are first seated in position in the insulator 12, then the insu.- lators 31 are ut in place. The terminals are temporarily eld in place by special centering ins secured to the 'sup rting fixture, whic pins are inserted in t e a rtures in the terminals and insulators 31 w ile the resistance conductor is stretched and secured around the projections 15, 16 and 35. Then the sheath 13 is slipped endwise over the insulator 11, which fits loosely inthe sheath to provide ease in assembly and along over the resistance conductor an over the insulator 12 in proper position the centering ins previously referred to being remove as the sheath is slipped over the insulator 12. With the sheath 1n position the insulators 32 and 34 are put in place, and then the two terminal pins 29 and 30, are screwed tightly into their respective terminals, whereby the terminal pins and the terminals are secured to the sheath. The indentation 39 is then made in the sheath to secure the insulator 11 against movement due to the tension of the resistance conductor which wasstretched durinlg assembly to properly separate its turns. he clips 40 and 41 are then removed and the end of the sheath struck down adjacent the insulator 12 so as to tightly close it, 'an eyelet 42 being inserted to secure the two sldes together.

In the next step the sheath 13 is held with the insulator l1 uppermost and the powdered insulating material 14 is poured into it, the sheath being suitably vibrated to shake the insulating material down through the grooves or slots 43 and 44 in the insulator 11 into the central space around the len hs of the resistance conductor. This vi rating action also serves to compact the insulating material somewhat and when the sheath has been filled this end is struck down to tightly close it and Secured with an eyelet 45. The last step is the reduction of the cross sectional area of the sheath in order to com act the insulating material. This is done y depressing the upper side of the sheath between the insulators and by striking longitudinal de ressions or troughs in the upper side o the sheath between the lengths of the resistance conductor, this being done preferably by means of a die. As shown, three depressions 46, 47 and 48 are provided although, if desired, the middle one 47 may be omitted. This compacts the powdered insu'latingfmaterial around the resistance conductor while at the same time leaving the lower face 49 of the heater as a plane surface so that it may be secured to a flat object in good heat conducting relation therewith. The heater may be attached to the part to be heated by means of screws passed through the eyelets 42 and 45.

In Fig. 7 I have shown a modified form of my invention in which a porcelain insulator 50 is provided on the exterior of the heater in place of thel insulators 31 and 34 of F igs. 1 to 6 inclusive. The particular form shown is for a heater in which the terminals are brought out at opposite ends of the heater, and consequently in order to secure the insulator against turning the sheath 51 is provided with extruded projections v52 and 53 which lit in recesses in the insulator. A gasket 54 is provided between the insulator and the'sheath. In other respects the construction isvvery similar to that shown in Fig. 2. Like the arrangement of Fig. 2, the terminal parts are secured together by screwing the tei -ninal pins into their respec-v tive terminal members 24. A lock washer 55 is provided for the terminal pin, this washer being rectangular and seated in a recess 56 in the top of the insulator. After the terminal pin has been screwed down tightly one end of the washer is bent up against one side of the square head of the terminal lug as indicated by the reference character 57.

The porcelain insulator may also be used with the type of unit shown in Figs. 1 to 6 inclusive wherein both terminals are brought out at one end of the unit. In this case, however, a single insulator is provided which is secured by the two terminal pins against turning so that the extruded portions 52 and 53 in the casing and the recesses in the insulator need not be provided.

What I claim as new and desire to secure by Letters Patent of the United States is z- 1. An electric heater comprising an elongated metallic sheath, a pair of insulators in said sheath adjacent the ends thereof, a resistance conductor extending in a plurality of lengths between said insulators, one of said insulators being provided with recesses and the other of said insulators being provided with a protuberance around which the resistance conductor is looped, terminal members seated in said recesses, said terminal members being provided with tapped apertures, connections between said resistance conductor and said members, and threaded terminal pins extending through said sheath into said apertures whereby said members and said terminal pins are clamped securely to said sheath and granular insulating material in said sheath compacted around said resistance conductor.

2. An electric heater comprising a metallic sheath having an elongated cross section and provided with side apertures at one end, a pair of insulators in spaced relation in said sheath, one of said insulators being provided with recesses registering with the apertures in said sheath, terminal members in said recesses, said terminal members being provided with tapped apertures registering with the apertures in said sheath, terminal pins extending through said apertures into threaded engagement with the apertures in said terminal members whereby said terminal members and said terminal pins are secured to said sheath, insulators between said sheath and said terminal members and terminal pins, a resistance conductor in said sheath extending in a plurality of substantially parallel lengths between said insulators, said insulators being provided with grooves forming protuberances around which said resistance conductor is looped so as to be secured by said insulators, connections between the ends of said resistance conductor and said terminal members, and compacted granular insulating material in said sheath embedding said resistance conductor, said sheath being provided with longitudinal extending depressions between the lengths of said resistance conductor.

3. An electric heater comprising an insulator provided with a recess, a terminal mem ber fitting in said recess, an elongated sheath having one end fitting over said insulator so as to secure said terminal member in said recess, an electrical insulator between said terminal member and said sheath, said terminal member being provided with a threaded aperture and said sheath being provided with an aperture in its side wall registering with the aperture in said terminal member, a terminal pin extending through the aperture in said sheath into threaded engagement with said terminal member, a shoulder on the outer end of said terminal pi-n, an insula- 

